Field of the Invention
The present invention relates to document stacking, and especially to envelope stacking in a mail sorting machine.
There are existing mail handling machines which are utilized for processing letter mail from the U.S. Post Office as it is received from the public. The letter mail received from the public is infinitely variable in respect to size and weight. For this reason alone, it becomes increasingly difficult to handle the letter mail, as it is generally placed into a stack for feeding from or subsequently being directed to an area where stacking of the letter mail takes place.
Typically, mixed letter mail is fed through a mail sorting machine which separates each mail piece so that there is a vertically oriented stream of mail progressing along a conveyor towards an optical code reading device which reads the address. Immediately thereafter, each mail piece is imprinted with a bar code representing the address zip code commensurate with a determined verification of the address zip code as checked by a cooperating computer which is connected to the mail sorter.
The OCR mail sorter processes letter mail at 128 inches per second. There are OCR mail sorters having as many as 60 sorting bins and as few as 12. Typically, each bin holds up to 425 average sized envelopes.
There is a need to have a substantial stacking capacity in each sorting bin since the sorter production rate is high, and since many of the machines in the field have the larger number of bins, it becomes necessary to be concerned about keeping the bins unloaded without down time when the machine is running.
It is particularly desirable to have great reliability in handling the envelopes as they are conveyed, approach, and are pushed into the stacking bins, against the supporting abutment member located on the stacking support of the stacker bin. If there are jams in this area of the machine, there is a great potential for damaging the envelopes, in addition to causing machine down time. Unfortunately, the present designs for envelope stackers have not provided the reliability required to address the jam problem, and in addition the design of the stackers remain complicated without eliminating the jam problems. For example, in one envelope stacking apparatus, an envelope abutment member rests upon a conveyor belt which is horizontally disposed beneath the upstanding envelopes. When the envelopes develop a pushing force at the input gate of the stacker, they push a sensing lever pivotally mounted at the input gate. Often, the sensing device causes the envelopes to travel or become skewed in a vertical plane with respect to the conveyor path, thereby causing a jam. A switch is then actuated which in turn energizes a motor connected to the conveyor belt to move the envelope abutment member a distance commensurate with the distance moved by the sensing lever and so forth. The problem with this system lies in the response time since there is a rapid accumulation of envelopes during the cycle time described, which leaves a potential for a jam by not allowing envelopes to move from the input gate during the time interval when the abutment member is stationary and then caused to move.
Another device applied to the envelope stacking apparatus to provide a uniform force to the envelope abutment member is a sash weight and pulley system. The sash weight is operatively connected to a cable which is supported on guide pulleys. When the envelopes enter the stacking bin, an accumulation of them provides a pushing force which subsequently pushes back the envelope abutment member. There is also some form of mechanical pushing device such as a brush at the input gate which keeps the envelopes moving towards the envelope abutment member. The problem with this system is that it is bulky, and particularly cumbersome and there is a potential that the cable will break, thereby permitting the envelope abutment member to slam and be damaged against its stop. This situation then presents a further potential for losing the use of the machine.
Therefore, it is intended that the present invention eliminate the foregoing mentioned problems with increased reliability, better response, versatility, and application of a uniform resisting force to the envelope stack to eliminate jams at the input side of the envelope stacker.